Apparatus for cleaning dust-laden gases



Feb. 16, 1965 E. KRANTZ APPARATUS FUR CLEANING DUST-LADEN GASES FiledJune 11, I963 HEATER mvzu'ronz EVERT K RANTZ ATTYS.

United a O 3,170,007 APPARATUS FOR DUST-LADEN Evert Krantz, Stockholm,Sweden, assignor to Aktiebolaget Svenska Flaktfabriken, Stockholm,Sweden, a corporation of Sweden Filed June 11, 1963, Ser. No. 287,017

Claims priority, application Sweden, Dec. 23, 1960, 12,498/ 60 4 Claims.(Cl. 261-136) This invention relates to an apparatus for cleaningdustladen gases and has for an object theprovision of improvements inthis art. Cleaning is efiected by wet-purification which produces anagglomeration of dust particles by a special use of finely atomizedwashing liquidinto the dust-laden gas and the subsequent precipitationof the agglomerated dust and liquid particles. This application is acontinuation-in-part of my copending application Serial No. 161,017,filed December 21, 1961, now abandoned; In part the invention makesv useof apparatus which is similar to that disclosed in my Patent No.2,883,167.

In order to obtain an optimum efiiciency in the separation of dustparticlesfrom theentraining gas it is essential in gas purifiers of theabove-mentioned type that intimate mixing of the washing liquid with thegas be obtained and also thatthe largest possible contact surface beobtained. This means that the washing liquid which is supplied must bebroken up into very fine particles since the efiiciency of the actionincreases as the particle size is reduced.

With centrifugal apparatus or compressed air nozzles heretoior'e usedfor the atomization of liquid, there are diificulties in securingthevery small particle size whichis desired Without unreasonably greatpower consumption.

and other disadvantages." To "be effective for removing I very fine dustparticles from gases, it is necessary to provide liquid particles'in the.orderof' about 20a. In order 2 plies to humidifying by circulatingWater .at 26 C. If the elficiency of cooling be taken to be 50%, thismeans that approximately 6 g. or 6 cm. of water/ kg. of gas is convertedduring condensation into particles of a size in the order M10 If 1 g. or1 cm. of water is broken up into particles of this size, it will providea total external.

. to 2.0 m? or a total of 12 m? of contactsurface/kg. of

to obtain particles of this small size by means of-cen-Q trifugalnozzles it is necessary to use a nozzle pressure as high as 150 kg./cm.and for compressed air nozzles the air must have a working pressure ashigh as 0.7 kg./crn.

V the nozzles if they are to withstand the wear and avoid clogging. Thelatter requirement is the most difficult to 1 meet and it has been foundpractically impossible to produce a reliable compressed air'nozzle fordust separation. The present invention eliminates the above-mentionedgas. In order to obtain particles of the last-mentioned size with theaid of centrifugal nozzles, a working pressure of not less than about1000 l g./cm. would be required.

The invention will now be described more in detail with reference tothe'accompanying drawing wherein:

The single figure is a somewhat diagrammatic vertical axial sectionthrough the gas inlet and liquid mixing portions of a wet purifier withliquid supply in two stages.

In the. drawing, the numeral 1 designates a collection chamber with agas outlet 1a at the top, a trapped liquid overflow 1b, and a sludgeclean-out chamber 1c. The,

numeral Z'designates, in general, the multi-stage venturitype gaspurifier provided in accordance with the present invention.

An inlet pipe '3 provides for the introduction of raw hot dust-laden gasto be purified into an expansion chamber 4 having a cylindrical upperportion 4a and a lower funnel-shaped portion 4b The upper portion 4a hasa diameter much greater than the diameter of the pipe 3 and the'pipe 3at the lower end terminates below the upper endof the funnel-shapedportion 4b but fully clear of the sides thereof. I

An .outlettube 5 of considerably smaller diameter than the inlet pipe 3is connected to and extends down from thebottom of the funnel-shapedportion 4b. An annular sharp-edged ledge 12 is provided at the lower endof the i n V funnel-shaped portion 4b to cause gas and liquid flowingThis places very exacting requirements on the design of g and otherdifiiculties by supplying liquid in at least two separate stages byspecialized, apparatus-of a simple, sturdy, effective and reliablecharacter.

In the first stage hot liquid is supplied into a gas ex- 1 pansion spacein such a way that the moisture from the waterfexists'largely in theform-of vapor. This has" the highly desirable efiect of producing aneffective temperature drop of'the-incoming hot gas so that the gas,independently of its inlet temperature, will always enter the next stageof treatment with a-substantially constant temperature and volume.

In a subsequent stage, after the hot gas has been "-reducedto'substantially constant temperature and volume and a substantiallysaturated condition in the first stage and supplied by a small-size tubeinto a second expansion chamber, the gas is cooled by theintermixingtherewith of finely divided particles of cold water toproduce a condensation of the vapor from the steam phase and aconsequent increase of the effective contact surface.

With the present treatment a considerable increase of the contactsurface of the liquid with the gas is obtained, as the followingexample'will illustrate. If the incoming gas'has a temperature of C. anda water content of 10 g./kg. of gas, the water content can beincreased'to 21 g/kg. of gas-an increase of ll'gi/kg. of gas. Thisapdownward thereover to flow inward with violent turbu lence, asdisclosed in my patent referred to above, to break A lower expansionchamber 6 has a cylindrical portion 6a which extends down from the top'end of the funnelshaped portion -4b and at the lower end of thecylindrical portion 6a there is provided a funnel-shaped portion 6b. Thelower end of the tube 5 terminates below the upper end of thefunnel-shaped portion 6b but fully clear'of the sides thereof.

An outlet difi'user tube 7 of the venturi type, and having an upperendconsiderably smaller than the tube 5, is connected to the lower end ofand extends down from the funnel-shaped portion 6b. An annularsharp-edged ledge 13 is provided at the lower end of the funnel-shapedportion 6b to cause gas and liquid flowing downward thereover to flowinward with violent turbulence to break the liquid up into very fineparticles and mix them thoroughly with the gas. The lower end of thedownwardly outfiaring tube 7 discharges liquid and gas below the surfaceof the body of liquid which is collected in the chamber 1. The tube 7expands downwardly to-reduce the velocity of the gas and avoid undueturbulence in the liquid in the'tank 1.

Liquid is supplied to the downflowing gas in two stages, I,

each into a body of expanding gas.

In the first stage, hot liquid is supplied through an inlet pipe 8 into,an annular trough 10 above the upper end of the funnel-shaped portion4bto flow down in'anannular sheet along the, conical surfaceof thefunnel-shaped portion 4b and discharge over the inner edge of theannular flange 12 into the body of fast-moving gases. An annular spaceis left between the'innerside of the annular trough 10 and the outsideof the inlet pipe 3. The liquid flowing down the funnel-shaped portion412 builds up in radial thickness above the annular flange 12 to assistin forcing the liquid inward into the high-velocity stream of gas. Meansfor heating the water is indicated at 14.

In the second stage, cold liquid is supplied through an inlet pipe 9into an annular trough 11 above the upper end of the funnel-shapedportion 6b to flow down in an annular sheet along the conical surface ofthe funnelshaped portion 6b and discharged over the inner edge of theannular flange 13 into the body of fast-moving gases. An annular spaceis left between the inner side of the trough 11 and the outside of theoutlet tube 5. The liquid flowing down the funnel-shaped portion 611builds up in radial thickness above the annular flange 13 to assist inforcing the liquid inward into the high-velocity stream of gas.

When the liquid flows down and inward over the sharpedged flanges 12 and13 it is broken up violently by the turbulence of the high-velocitygases flowing at a velocity in the order of 30 to 125 m./ sec.

The liquid supplied in the first stage is at a relatively hightemperature so that it readily vaporizes in the hot gas to form veryfine vapor particles. The presence of this body of vapor atapproximately the state of saturated steam, having a very largeheat-storage capacity, brings the mixture, of gas and vaporsubstantially to a constant temperature regardless of the temperature ofthe entering gas. Since the temperature is constant, the volume per unitof weight of the saturated gas will be substanti'ally constant.

Since the saturated gas provided in the first mixing chamber is at anapproximately fixed temperature it is readily chilled and condensed bythe cold water in the second stage, with good agglomerationof the fineparticles of liquid on the dust particles, which provides almostcomplete separation when the gas is flowed out through the water bothmaintained in the tank 1, pure clean gas flowing out at In for such usesas may be desired.

Because of the fact that the gas is cooled at each stage, its volume isreduced and the channels 3, and 7 of decreasing diameter are selectedaccordingly-to maintain the flow of gas at all stages near the samevelocityfor the better turbulence and break-up and mixing with the waterwhich is introduced.

The water at each stage is supplied at a reduced throat location where,on account of the restricted throat size the gas velocity is momentarilyat a maximum to produce the greatest turbulence, followed by anexpansion which causes good assimilation of the fine vapor particlesformed here and cooling of the gas by expansion.

It will now be seen that by the apparatus of use provided by theinvention the dust separation is very effectively produced by extremelysimple and inexpensive means. The hot dry gas which may. be supplied atvarying dry bulb temperatures is effectively saturated and brought toconstant temperature in the first stage and condensed and the'dustparticles agglomerated in the second stage. This provides gas flow atsubstantially constant rate at each mixing point, a condition favorableto the most effective particle break-up and difiusion.

While one embodiment of the invention has been described for purposes ofillustration, it will be understood that there may be variousembodiments and modifications within the general scope of the invention.

1 claim:

1. Apparatus for the wet-purifiction of hot dust-laden gases, comprisingin combination: a first expansion chamber, a gas supply conduitextending down into said first expansion chamber, a second expansionchamber disposed below' said first expansion chamber, a convergentbottom for said first expansion chamber, a first mixing conduitextending from the bottom of said convergent bottom into said secondexpansion chamber, a convergent bottom for said second expansionchamber, a second mixing conduit extending downward from the bottom ofthe second expansion chamber, inwardly projecting flanges at the upperends of each of said mixing conduits,'means to supply hot liquid aroundthe outer periphery of said first expansion chamber above the upper endof said convergent bottom to flow down in an annular film over saidconvergent bottom and inward over said flange to break up in the violentturbulence of the hot gas flowing at high velocity over said flange, andmeans to supply cold liquid around the outer periphery of said secondexpansion chamber above the upper end of said convergent bottom to flowdown in an annular film over said convergent bottom and inward over saidflange to break up in the violent turbulence of the gas flowing at highvelocity over said flange, the entire flow of gas and liquid beingconfined to pass through said mixing conduits, said conduits beingsuccessively of smaller size downward to take account of reduced gasvolume and provide high velocity gas flow through said conduits.

2. Apparatus as set forth in claim 1, further characterized by the factthat said second mixing conduit has its lower end formed of increasingsize downward and has its lower end submerged in liquid.

pansion chamber having a funnel-shaped lower end por tion and arestricted bottom outlet tube with an inwardly projecting annular flangeat its upper end; means for supplying hot water to the top of saidfunnel-shaped portion to flow downward in an annular film thereon andover said annular flange, said outlet tube being of a smaller diameterthan said supply pipe to compensate for cooling of the gas and providehigh velocity flow past said annular flange to atomize the water and mixit in said gas; a second expansion chamber having a funnel-shaped lowerend portion and a restricted lower bottom outlet tube with an inwardlyprojecting annular flange at its upper end; means for supplying coldwater to the top of said funnel-shaped portion to flow downward in anannular film thereon and over said annular flange, said lower outlettube being of a smaller diameter than the first said outlet tube tocompensate for cooling of the gas in said second expansion chamber andprovide high velocity flow past said. anular flange to atomize the waterand mix it with the gas, and means providing a body of water for theoutflow of gas from said lower outlet tube.

4. Apparatus for cleaning hot dry dust-laden gases,- oomprising incombination, a gas supply pipe, a first expansion chamber having afunnel-shaped lower end portion anda restricted bottom outlet tube withan inwardly projecting annular flange at its upper end; means forsupplying hot water to the top of said funnel-shaped portion to flowdownward in an annular film thereon and over said annular flange, asecond expansion chamber having a'funnel-shaped lower end portion and arestricted lower bottom outlet tube with an inwardly projecting annularflange at its upper end; means for supplying cold water to the top ofsaid funnel-shaped portion to flow downward in an annular film thereonand over said annular flange, and means providing a body of water forthe outflow of gas from said lower outlet tube, said lower outlet tubeexpanding in diameter downward to minimize turbulence in the body ofwater at its outlet.

References Cited by the Examiner UNITED STATES PATENTS 1,182,543 5/16Ferguson 5590 1,844,851 2/32 Harmon 5594. 2,883,167 4/59 Krantz 261-46,

NORMAN YUDKOFF, Primary Examiner. REUBEN FRIEDMAN, Examiner.

1. APPARATUS FOR THE WET-PURIFICATION OF HOT DUST-LADEN GASES,COMPRISING IN COMBINATION: A FIRST EXPANSION CHAMBER, A GAS SUPPLYCONDUIT EXTENDING DOWN INTO SAID FIRST EXPANSION CHAMBER, A SECONDEXPANSION CHAMBER DISPOSED BELOW SAID FIRST EXPANSION CHAMBER, ACONVERGENT BOTTOM FOR SAID FIRST EXPANSION CHAMBER, A FIRST MIXINGCONDUIT EXTENDING FROM THE BOTTOM OF SAID CONVERGENT BOTTOM INTO SAIDSECOND EXPANSION CHAMBER, A CONVERGENT BOTTOM FOR SAID SECOND EXPANSIONCHAMBER, A SECOND MIXING CONDUIT EXTENDING DOWNWARD FROM THE BOTTOM OFTHE SECOND EXPANSION CHAMBER, INWARDLY PROJECTING FLANGES AT THE UPPERENDS OF EACH OF SAID MIXING CONDUITS, MEANS TO SUPPLY HOT LIQUID AROUNDTHE OUTER PERIPHERY OF SAID FIRST EXPANSION CHAMBER ABOVE THE UPPER ENDOF SAID CONVERGENT BOTTOM TO FLOW DOWN IN AN ANNULAR FILM OVER SAIDCONVERGENT BOTTOM AND INWARD OVER SAID FLANGE TO BREAK UP IN THE VIOLENTTURBULENCE OF THE HOT GAS FLOWING AT HIGH VELOCITY OVER SAID FLANGE, ANDMEANS TO SUPPLY COLD LIQUID AROUND THE OUTER PERIPHERY OF SAID SECONDEXPANSION CHAMBER ABOVE THE UPPER END OF SAID CONVERGENT BOTTOM TO FLOWDOWN IN AN ANNULAR FILM OVER SAID CONVERGENT BOTTOM AND INWARD OVER SAIDFLANGE TO BREAK UP IN THE VIOLENT TURBULENCE OF THE GAS FLOWING AT HIGHVELOCITY OVER SAID FLANGE, THE ENTIRE FLOW OF GAS AND LIQUID BEINGCONFINED TO PASS THROUGH SAID MIXING CONDUITS, SAID CONDUITS BEINGSUCCESIVELY OF SMALLER SIZE DOWNWARD TO TAKE ACCOUNT OF REDUCED GASVOLUME AND PROVIDE HIGH VELOCITY GAS FLOW THROUGH SAID CONDUITS.